This invention relates to the field of heat treatment of various metals to enhance their strength, resiliency, and the like. In the past, the materials have been treated, for various time periods, in heat treating ovens, in air, in vacuum, or in the presence of selected gases, at high temperatures. The treatment is usually carried out in specially designed ovens in which the materials to be treated are held on carrying racks or carrying baskets.
As the heat treating field has developed in recent years, treating temperatures have increased. It has been found that treatment at higher temperatures both improves the treatment and decreases the length of treatment time. These higher temperatures, however, have provided problems because the materials out of which the baskets and racks have been made have been unable to withstand the temperatures used and retain structural integrity.
Prior racks and baskets have been made of various nickel-chromium alloys. These lose their strength at temperatures such as 2,300.degree. F., a temperature which is not uncommon today. The industry, therefore, has gone to the use of materials such as molybdenum, which has a melting point of about 4,800.degree. F. Molybdenum, however, crystallizes and becomes brittle when raised to temperatures higher than about 1,800.degree. F. Consequently, though baskets and racks made of molybdenum can be used, they will become very brittle and, if dropped, are likely to shatter. Since molybdenum is an expensive metal, the baskets and racks have had to be handled carefully, and, regardless, usually do not enjoy a very long life span before breakage.
In addition, in the making of racks and baskets, bars or rods of the metal used have to be welded together. This high temperature welding, by itself, can cause crystallization of molybdenum at the weld points, making the baskets brittle, even before their first use in high temperature ovens.